The latest idea comes from member Twilight_Fenrir, who suggests that what we're seeing in that image might be in fact a reference to an ancient Norse legend - that of Fenrir.
Twilight_Fenrir says: "I was looking at that new picture... and one idea immediately leapt out at me... And that is how much this image reminded me of Fenrir, or, the Fenris Wolf..."
Fenrir was a giant wolf that for a very long time, like Twilight says, was bound by a chain on the Island of Lyngvi.
Now, what's really curious is a little detail found on the Wikipedia article, which has similarities to what we're seeing in the shot.
"When the Æsir saw that the Wolf was fully bound, they took the chain that was fast to the fetter, and which is called Gelgja 'Thin', and passed it through a great rock-it is called Gjöll 'Scream'-and fixed the rock deep down into the earth. Then they took a great stone and drove it yet deeper into the earth-it was called Thviti-and used the stone for a fastening-pin. The Wolf gaped terribly, and thrashed about and strove to bite them; they thrust into his mouth a certain sword: the guards caught in his lower jaw, and the point in the upper; that is his gag. He howls hideously, and slaver runs out of his mouth: that is the river called Ván 'Hope'; there he lies till the Twilight of the Gods." (as translated by Arthur G. Brodeur)
Could that shadow at the top of the picture belong to Fenrir, or at least a giant wolf? Lots to ponder about there.